1. Field of the Invention
The present invention relates to a method for manufacturing high modulus and low shrinkage industrial polyester fibers useful as materials for reinforcing rubber products, such as a tire and a belt, with high spinning efficiency so that polyester fibers have uniform physical properties.
Particularly, the invention pertains to a method for manufacturing polyester fibers comprising the steps of: melt-extruding a polymer without increasing an intrinsic viscosity IV of the polymer during spinning to minimize a reduction of the intrinsic viscosity of the polymer; winding the polymer at 2,000 m/min or more to produce an undrawn yarn, followed by drawing the undrawn yarn through three stages at a temperature of glass transition (Tg) or less; wherein polyester fibers with uniform fineness and physical properties can be manufactured with high spinning efficiency by setting eddy plates A directly below a nozzle. A dipped cord produced by twisting and dipping polyester fibers according to the present invention has a high strength and an excellent dimensional stability.
2. Description of the Prior Art
As well known in the art, high tenacity polyethylene terephthalate filaments are useful in industrial applications, such as a tire cord for reinforcing rubber, a seat belt, a V-belt, and a hose. Efforts have been made to improve physical properties of a high tenacity industrial yarn, in particular, a toughness of a treated cord and a dimensional stability, useful as a fiber reinforcement in a rubber tire.
Generally, a yarn having E-S of 7.0 to 8.0% and an excellent dimensional stability, used as materials for reinforcing rubber products such as a tire and a belt, which is used to manufacture a HMLS (High Modulus Low Shrinkage) dipped cord, is produced by extruding a molten polyester polymer through a nozzle, cooling the molten polyester through a solidification region, in which a separate heating device (e.g. a heated sleeve at 150 to 450° C.) is set, winding the resulting polyester at 2,000 m/min or faster, and drawing it at a temperature of glass transition (Tg) or higher, as shown in FIG. 3. According to the prior arts, a portion of cooling air passing through multifilament bundles forms a vortex directly below a nozzle. Also a portion of extruded filaments is rapidly quenched by the vortex to generate curved filament or fused filament to create an uneven fineness of a yarn and nonuniform physical properties of a yarn, and broken filament are formed due to nonuniform physical properties of filaments during the drawing, thereby a spinning efficiency is reduced.